As a common staple is driven from a rack of staples in a desktop stapler, the legs of the staple can become bent or curled from contacting the paper stack in a non-perpendicular manner. One leg can become angled inward due to a lack of support along the interior of the staple legs. The exterior of the staple legs, however, is supported typically by the housing walls of the staple chamber that prevent the legs from accidentally flaring outward before the points of the leg penetrate the surface of the paper stack.
If a staple leg bends inward prior to penetrating the surface of the paper stack, as the staple is driven through the paper, the leg that is bent inward cannot support the forces on top of the staple, which can cause the staple, the staple leg, or both to buckle, or the leg may be pinched inward. This can result in poor or non-existent clinching of the paper stack by that staple. On the other hand, once the staple legs have penetrated the top surface of the paper stack, the legs are thereby stabilized by the paper and the legs can continue to pass straight through the paper stack and into the anvil underneath for a normal clinched configuration.
Some conventional, non-spring energized desktop staplers have a track design that supports the interior and exterior of the staple legs. Typically, an inner staple track is connected to an outer staple track using a very strong and stiff spring that holds the inner track under the staple as the staple is driven into the paper stack. The staple, as it is driven, forces the inner track rearward away from the staple path and allows the staple to be driven into the stack of paper. The staple guide feature is incorporated into the front end of the inner track and the inner and outer tracks move in unison as the staple is driven into the paper stack.
In the conventional design, the staple leg guide/inner track is forced rearward away from the staple being driven as soon as that staple is sheared from the rack, but before the staple leg points have penetrated the surface of the paper stack. As a result, there needs to be a very large biasing force against the inner track, urging it toward the driven staple. If there is only a small biasing force, the inner track can be moved rearward from the momentum generated by the impact with the driven staple, which again occurs before the staple points have penetrated the paper. Conventional designs that suggest a large biasing force on the inner track urging it toward the driven staple in order to resist this rearward momentum and to maintain the staple leg guide/inner track in position to guide the staple legs perpendicularly into the paper stack.
An example of a staple guide is disclosed in U.S. Pat. No. 4,151,944 (Picton). Picton teaches a “shoe” that is designed to guide the interior of the legs of a staple.